Clarify template selection resolution

ui/src/dashboards/actions/index.ts

@@ -19,9 +19,9 @@ import {notify} from 'src/shared/actions/notifications'
 import {errorThrown} from 'src/shared/actions/errors'
 
 import {
-  applySelections,
+  applyLocalSelections,
   templateSelectionsFromQueryParams,
-  queryParamsFromTemplates,
+  templateSelectionsFromTemplates,
 } from 'src/dashboards/utils/tempVars'
 import {validTimeRange, validAbsoluteTimeRange} from 'src/dashboards/utils/time'
 import {
@@ -584,7 +584,7 @@ export const getDashboardWithTemplatesAsync = (
       .map(t => hydrateTemplate(proxyLink, t, []))
   )
 
-  applySelections(nonNestedTemplates, templateSelections)
+  applyLocalSelections(nonNestedTemplates, templateSelections)
 
   const nestedTemplates = await Promise.all(
     dashboard.templates
@@ -592,7 +592,7 @@ export const getDashboardWithTemplatesAsync = (
       .map(t => hydrateTemplate(proxyLink, t, nonNestedTemplates))
   )
 
-  applySelections(nestedTemplates, templateSelections)
+  applyLocalSelections(nestedTemplates, templateSelections)
 
   const templates = [...nonNestedTemplates, ...nestedTemplates]
 
@@ -615,7 +615,7 @@ export const rehydrateNestedTemplatesAsync = (
       .map(t => hydrateTemplate(proxyLink, t, dashboard.templates))
   )
 
-  applySelections(nestedTemplates, templateSelections)
+  applyLocalSelections(nestedTemplates, templateSelections)
 
   dispatch(updateTemplates(nestedTemplates))
   dispatch<any>(updateTemplateQueryParams(dashboardId))
@@ -627,7 +627,7 @@ export const updateTemplateQueryParams = (dashboardId: number) => (
 ): void => {
   const templates = getDashboard(getState(), dashboardId).templates
   const updatedQueryParams = {
-    tempVars: queryParamsFromTemplates(templates),
+    tempVars: templateSelectionsFromTemplates(templates),
   }
 
   dispatch(updateQueryParams(updatedQueryParams))

ui/src/dashboards/utils/tempVars.ts

@@ -4,7 +4,7 @@ import qs from 'qs'
 import {formatTempVar} from 'src/tempVars/utils'
 
 import {Template, TemplateQuery} from 'src/types'
-import {TemplateQPSelections} from 'src/types/dashboards'
+import {TemplateSelections} from 'src/types/dashboards'
 
 export const makeQueryForTemplate = ({
   influxql,
@@ -17,7 +17,7 @@ export const makeQueryForTemplate = ({
     .replace(':measurement:', `"${measurement}"`)
     .replace(':tagKey:', `"${tagKey}"`)
 
-export const templateSelectionsFromQueryParams = (): TemplateQPSelections => {
+export const templateSelectionsFromQueryParams = (): TemplateSelections => {
   const queryParams = qs.parse(window.location.search, {
     ignoreQueryPrefix: true,
   })
@@ -29,7 +29,9 @@ export const templateSelectionsFromQueryParams = (): TemplateQPSelections => {
   )
 }
 
-export const queryParamsFromTemplates = (templates: Template[]) => {
+export const templateSelectionsFromTemplates = (
+  templates: Template[]
+): TemplateSelections => {
   return templates.reduce((acc, template) => {
     const tempVar = stripTempVar(template.tempVar)
     const selection = template.values.find(t => t.localSelected)
@@ -45,18 +47,22 @@ export const queryParamsFromTemplates = (templates: Template[]) => {
   }, {})
 }
 
-export const applySelections = (
+export const applyLocalSelections = (
   templates: Template[],
-  selections: TemplateQPSelections
+  selections: TemplateSelections
 ): void => {
+  // Ensure that every supplied template has an appropriately set
+  // `localSelected` value.
   for (const {tempVar, values} of templates) {
     if (!values.length) {
       continue
     }
 
+    // Attempt to use supplied selection
     let selection = selections[tempVar]
 
     if (!selection || !values.find(v => v.value === selection)) {
+      // Default to template's `selected` value if no valid selection is found
       selection = values.find(v => v.selected).value
     }
 

ui/src/types/dashboards.ts

@@ -135,7 +135,7 @@ export interface DashboardSwitcherLink {
   to: string
 }
 
-export interface TemplateQPSelections {
+export interface TemplateSelections {
   // e.g. {':my-db:': 'telegraf'}
   [tempVar: string]: string
 }